This invention relates to an improvement of oil cooler built in a radiator for cooling oil for a torque converter or for engine lubrication.
In a conventional oil cooler built in an radiator as shown in FIG. 1, a tubular oil cooler is fitted in a lower tank 2 (horizontal tank in case of horizontal flow type radiator) of a radiator 1, and within said cooler 3, oil for a torque converter and for engine lubrication and the like are circulated by way of oil ducts 4, 5 which are communicated with said cooler 3, and the oil is cooled by cooling water for engine. Such an oil cooler is in principle as shown in FIG. 2, wherein an inner tube 7 is inserted in an outer tube 6, expanded ends 8 of the inner tube 7 are closely attached to the outer tube 6, oil ducts 4, 5 are communicated with oil space 15 formed between the outer and inner tubes 6, 7 watertightly penetrating the wall of lower tank with packings 9, 10 to circulate oil within said cooler, thus to cool oil flowing through said oil space by cooling water inside of the inner tube 7 and outside of the outer tube 6. In fact, for the purpose of improving heat transfer rate of such an oil cooler, usually, as shown in FIG. 3, fins 11 are inserted between the outer tube 7 and the inner tube 7, and as shown in FIG. 4 to FIG. 7, dent portions 12, 12 and 12a, 12a, which are respectively making a pair, are alternately formed on upper and lower sides as well as right and left sides as an inner tube 7, which tube is inserted in the outer tube 6 so as to leave a gap 13 between the inner tube side without dent portions and the outer tube 6, so that the oil flowing through the oil space 15 between the inner and outer tubes was disturbed. In such a usual construction, when fins are inserted therein, it becomes not only complicated, requiring much time and high cost, but also straight flow of oil is increased, resulting in poor heat transfer rate, and when an inner tube 7 provided with dent portions 12, 12, 12a and 12a is used, deformation of flat portions 7a, 7b formed by said dent portions 12, 12, 12a and 12a due to oil pressure flowing within the oil cooler becomes large, resulting in damage due to the fatigue of material.